In an effort to improve engine power, lower engine emissions, and reduce consumption of fossil fuels, it has been proposed to operate internal combustion engines with more than one type of fuel so that desirable attributes of the different fuels may be leveraged. In European Patent EP2048339 a mixture of gasoline and alcohol is separated into two fuels; the first having a higher concentration of gasoline, and the second having a higher concentration of alcohol. The alcohol fuel is then routed to a fuel reformer and converted to reformate comprised of H2, CO, and N2. The reformate may then be directed to the engine intake system so that cylinder dilution may be increased.
The inventor herein has also recognized that it is possible that vaporized ethanol may be routed to the engine rather than reformate during conditions of low fuel reformer efficiency or during degradation of the fuel reformer. If vaporized alcohol is routed to the engine rather than reformate, the engine exhaust gas oxygen concentration may deviated from a desired concentration. Further, the engine may begin to knock or misfire because vaporized alcohol may be less beneficial for improving combustion stability and knock mitigation as compared to reformate.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for improving engine air-fuel control of an engine having a fuel reformer. One embodiment of the present description includes a method for operating an engine, comprising: operating an engine by injecting a first liquid fuel; processing a second liquid fuel in a fuel reformer to produce a gaseous fuel; ramping in an injection amount of said gaseous fuel to said engine; and adjusting an actuator to a first state in response to said gaseous fuel when said gaseous fuel is a first type of gas; and adjusting said actuator to a second state in response to said gaseous fuel when said gaseous fuel is a second type of gas, said engine operating at substantially a same engine speed and load when adjusting said actuator.
By slowly ramping in injection of an unknown fuel to an engine, it may be possible to ascertain the fuel composition so that engine exhaust gas oxygen concentration deviates less. In this way, it may be possible to maintain or at least reduce efficiency losses of exhaust after treatment devices that may relate to the introduction of a gaseous fuel to the engine. Further, by adjusting an engine actuator in response to the detected fuel composition, it may be possible to limit cylinder charge dilution and cylinder charge capacity so that the engine has fewer propensities to knock or misfire. Thus, engine air-fuel control for an engine having a fuel reformer may be improved, at least under some conditions.
The present description may provide several advantages. Specifically, the approach may improve engine air-fuel control. Further, the method may better leverage attributes of different fuels output by a fuel reformer. Further still, the method allows the engine to operate at an output level that is related to the fuel type output from fuel reformer.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.